1. Field of the Invention
The present invention relates to an apparatus for sensing capacitance, a method for sensing capacitance, and a touch screen apparatus capable of minimizing an error occurring during detecting a change in capacitance due to noise.
2. Description of the Related Art
A touch sensing apparatus, such as a touch screen, a touch pad, and the like, is an input apparatus that is attached to a display apparatus to provide an intuitive input method to a user and has, in recent times, been prevalently applied to various electronic apparatuses such as mobile phones, personal digital assistants (PDAs), navigation devices, and the like. In particular, as demand for smart phones has recently increased, the use of a touch screen as a touch sensing apparatus capable of providing various input methods in a restricted form factor has been increased on a daily basis.
Touch screens applied to mobile devices may largely be classified into resistive-type touch screens and capacitive-type touch screens, according to a method of sensing a touch input utilized therein. Among the touch screens, the use of capacitive-type touch screens has been gradually increased owing to a relatively long lifespan, various input methods, easy implementation of gestures, and the like. In particular, a multi-touch interface may be more easily implemented in capacitive-type touch screens than in resistive-type touch screens, and as a result, has been widely applied to devices such as smart phones, and the like.
The capacitive-type touch screen includes a plurality of electrodes having a predetermined pattern, wherein a plurality of nodes in which a change in capacitance occurring due to a touch input is provided by the plurality of electrodes. The self-capacitance or mutual-capacitance of the plurality of nodes distributed on a two-dimensional plane may be changed by the touch input. Here, a weight average calculation method, and the like, may be applied to the change in capacitance occurring in the plurality of nodes to calculate coordinates of a touch input. In order to accurately calculate the coordinates of a touch input, a technology of accurately sensing the change in capacitance that occurs due to a touch input is required. However, when electrical noise occurs in a wireless communication module display apparatus, or the like, a change in capacitance cannot be accurately sensed.
Patent Document 1 discloses a circuit and a method for measuring capacitance of a touch sensor, in which a voltage of a capacitor charged from a change in capacitance occurring in a touch sensor is compared with a predetermined reference voltage, but does not describe removing a change in capacitance due to noise therefrom. Further, Patent Document 2 discloses a circuit for measuring capacitance but only discloses canceling an offset using a plurality of switches and it does not disclose removing a change in capacitance occurring due to noise.